1. Technical Field
The present invention relates to an optical device, which enlarges an exit pupil of a viewer system, and a virtual image display apparatus including the corresponding optical device.
2. Related Art
In the related art, virtual image displays for displaying a virtual image in an enlarged manner have been studied. However, since the exit pupil diameter of a single image device such as a liquid crystal panel is small, there has been a demand for a pupil enlargement technique having an excellent efficiency with a simple configuration. Further, there has also been a demand for an increase in the angle of view displayed.
For example, in order to extract light from an optical device called a combiner, there has been proposed an apparatus using a diffraction grating (for example, U.S. Pat. No. 4,711,512). In U.S. Pat. No. 4,711,512, a diffraction grating, in which multiple inclined reflective faces are arranged, is used.
However, a structure of U.S. Pat. No. 4,711,512 is complex, and particularly it is difficult to manufacture a large-size virtual image display apparatus with a configuration of U.S. Pat. No. 4,711,512. Further, in the configuration of U.S. Pat. No. 4,711,512, a stripe caused by the diffraction grating may be seen, and thus image quality of a virtual image is lowered.